variable support cleanup

src/basic/engine_editor/shift_txt_down.s

@@ -0,0 +1,43 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+
+//
+// Shift the BASIC program down to cover the area of removed line
+//
+
+
+shift_txt_down:
+
+	// First byte of destination is OLDTXT
+
+	lda OLDTXT+0
+	sta memmove__dst+0
+	lda OLDTXT+1
+	sta memmove__dst+1	
+
+	// First byte of source is memmove__dst + .X
+
+	clc
+	txa
+
+	adc memmove__dst+0
+	sta memmove__src+0
+	lda memmove__dst+1
+	adc #$00
+	sta memmove__src+1
+
+	// Size is distance from source to the end of BASIC text (VARTAB)
+
+	lda VARTAB+0
+	sec
+	sbc memmove__src+0
+	sta memmove__size+0
+	lda VARTAB+1
+	sbc memmove__src+1
+	sta memmove__size+1
+
+	// Perform the copy
+
+	jmp shift_mem_down